Integrated circuitry fabrication includes deposition of material and layers over a substrate. One or more substrates are received within a deposition chamber within which deposition typically occurs. One or more precursors or substances are caused to flow to the substrate, typically as a vapor, to effect deposition of a layer over the substrate. A single substrate is typically positioned or supported for deposition by a susceptor. In the context of this document, a “susceptor” is any device which holds or supports at least one wafer within a chamber or environment for deposition. Deposition may occur by chemical vapor deposition, atomic layer deposition and/or by other means.
FIGS. 1 and 2 diagrammatically depict a prior art susceptor 10, and issues associated therewith which motivated some aspects of the invention. Susceptor 10 comprises a body 12 which receives a substrate 14 for deposition. Substrate 14 is received within a pocket or recess 16 of susceptor body 12 to elevationally and laterally retain substrate 14 in the desired position.
A particular exemplary system which motivated some of the inventive susceptor designs herein was a lamp heated, thermal deposition system having front and back side radiant heating of the substrate and susceptor for attaining desired temperature during deposition. FIG. 2 depicts a thermal deposition system having at least two radiant heating sources for each side of susceptor 10. Depicted are front side and back side peripheral radiation emitting sources 18 and 20, respectively, and front side and back side radially inner radiation emitting sources 22 and 24, respectively. Incident radiation from sources 18, 20, 22 and 24 typically overlap one another on the susceptor and substrate, creating overlap areas 25. Such can cause an annular region of the substrate corresponding in position to overlap areas 25 to be hotter than other areas of the substrate not so overlapped. Further, the center and periphery of the substrate can be cooler than even the substrate area which is not overlapped due to less than complete or even exposure to the incident radiation.
The susceptor is typically caused to rotate during deposition, with deposition precursor gas flows occurring along arrows “A” from one edge of the wafer, over the wafer and to the opposite side where such is exhausted from the chamber. Arrow “B” depicts a typical H2 gas curtain within the chamber proximate a slit valve through which the substrate is moved into and out of the chamber. A preheat ring (not shown) is typically received about the susceptor, and provides another heat source which heats the gas flowing within the deposition chamber to the wafer along arrows A and B. However even so, the periphery of the substrate proximate where arrows A and B indicate gas flowing to the substrate is cooler than the central portion and the right-depicted portion of the substrate where the gas exits.
Additionally, robotic arms are typically used to position substrate 14 within recess 16. Such positioning of substrate 14 does not always result in the substrate being positioned entirely within susceptor recess 16. Further, gas flow might dislodge the wafer such that it is received both within and without recess 16. Such can further result in temperature variation across the substrate and, regardless, result in less controlled or uniform deposition over substrate 14.
The above-described system can be used for silicon deposition, including amorphous, monocrystalline and polycrystalline silicon, as well as deposition of silicon mixed with other materials such as a Si—Ge composition in any of crystalline and amorphous forms. Certain aspects of the invention were motivated relative to issues associated with selective epitaxial silicon deposition. In such deposition, a substrate to be deposited upon includes outwardly exposed elemental silicon containing surfaces as well as surfaces not containing silicon in elemental form. During a selective epitaxial silicon deposition, the silicon will preferentially/selectively grow typically only over the silicon surfaces and not the non-silicon surfaces. In many instances, near infinite selectivity is attained, at least for the typical thickness levels at which the selective epitaxial silicon is deposited or grown.
An exemplary prior art method for depositing selective epitaxial silicon includes flows of dichlorosilane at from 50 sccm to 500 sccm, HCl at from 50 sccm to 300 sccm and H2 at from 3 slm to 40 slm. An exemplary preferred temperature range is from 750° C. to 1,050° C., with 850° C. being a specific example. An exemplary pressure range is from 5 Torr to 100 Torr, with 30 Torr being a specific example. Certain aspects of the invention also encompass selective epitaxial silicon-comprising deposition using the just-described prior art process (preferred), as well as other existing or yet-to-be developed methods.
An exemplary prior art susceptor comprises graphite completely coated with a thin layer (75 microns) of SiC. Such graphite typically has a thermal conductivity of from 180-200 W/mK, while that of SiC is about 250 W/mK. Unfortunately, a selective epitaxial silicon process such as described above will also deposit upon silicon carbide in addition to elemental form silicon. Accordingly, the susceptor also gets deposited upon during a selective epitaxial silicon deposition over regions of a substrate desired to be deposited upon received by the susceptor. This is undesirable at least for purposes of temperature control of the substrate during deposition.
For example, consider that the deposition chamber used in the above-described processing includes upper and lower transparent domes or chamber walls which in part define the internal chamber volume within which deposition occurs. Such domes are transparent to incident infrared radiation, with the lamps which heat the susceptor and substrate being received external of the chamber and domes, with light passing therethrough to provide desired temperature during the deposition. Further, temperature control typically includes the sensing of the temperature of the back side of the susceptor using optical pyrometry techniques. For example, such comprises a non-contacting temperature sensing whereby a sensor received externally of the lower dome is directed to the back side of the susceptor and measures emissivity therefrom and from which the temperature of the susceptor and substrate are derived. However with the back side-growing silicon being of a different material than that of the underlying susceptor, such affects the emission/absorption characteristics of the thermal energy. Such tends to affect the sensing of the susceptor temperature to be reported lower than it actually is. Therefore as a silicon coating builds upon the back side of the susceptor, more energy is typically added to the heat lamps which undesirably increases the substrate temperature in a manner which is difficult to control. In other words, where the optical properties of the susceptor back side change where temperature is being sensed or measured, the measured temperature also changes as well although the temperature of the susceptor might essentially be the same as before the back side coating.
With the above just-described configuration, drift in process control can occur after processing from only 1 to 4 wafers. The accumulated silicon on the susceptor back side has caused a temperature drift of from 1° C. to 2° C. In order to maintain repeatability from wafer to wafer, present methods of contending with the same include a between wafer chamber dry-clean to etch the susceptor, as well as re-depositing a small amount of silicon on the susceptor to provide an initial uniform surface. Such processing can take about as long as processing a single wafer alone, and accordingly reduces throughput by about 50 percent. Yet without re-establishing the chamber to a similar baseline condition, wafer repeatability in the selective silicon deposition is poor.
It would be desirable to develop improved susceptor designs and methods which address at least some of the above-identified problems. However although some aspects of the invention were motivated from this perspective and in conjunction with the above-described reactor and susceptor designs, the invention is in no way so limited. The invention is only limited by the accompanying claims as literally worded, without interpretive or other limiting reference to the specification and drawings, and in accordance with the doctrine of equivalents.